Symbology readers, such as bar code readers, are well known. They are used in a wide range of applications, including inventory tracking and control. Most symbology readers utilize an illuminating light source which is swept across a symbology to generate a light signal indicative of the relative reflectivities of various scanned regions of the target object. Such swept or scanned systems are relatively complex due to their moving mirrors and related drive circuitry. They are also limited to scanning along a line, making application of such systems to two-dimensional symbology difficult and requiring raster scanning techniques.
With the advent of area type readers, requirements for illumination of the area of interest have changed. Rather than providing a fixed point of illumination to be swept across an area containing a symbology, area type readers typically require the entire area of a target object to be illuminated simultaneously.
One such method of illumination proposed in European Patent Application EPA 0 524 029 A2 utilizes flash optics formed from a xenon tube to provide an illuminated area approximately the same size as the imaged area. Such systems typically have relatively high power consumption and provide a fixed, non-uniform illumination pattern which is not easily adjustable no provide a desired illumination of a target object.
Moreover, a system such as that employing a single xenon tube typically provides an illumination pattern having its highest illumination normally in the center of the illuminated area and a reduced illumination near the perimeter of the illuminated area. Because many detector systems are most sensitive in their central regions and least sensitive around their perimeters, the sensitivity of such a xenon tube illumination system may be significantly reduced near the perimeter of the image area.